For automobiles, seal parts between car body opening peripheries, and opening/closing members for openings such as doors and trunk lids are used to prevent rain, wind and sounds from the outside. The seal parts commonly include a solid member attached to door frames, trunk lids, car body opening peripheries and the like, and a foamed member to seal gaps between car body opening peripheries, and opening/closing members for openings. The foamed member is required to be deformable to conform to irregularities and curved shapes of door frames, trunk lids and the like, and to have a hardness which allows close contact with door frames, trunk lids and the like.
U.S. Pat. No. 7,008,699 B2 discloses composite structures are described that include (a) a first polymer structure (e.g., a film or solid component) made of EPDM adhered to (b) a second polymer structure (film or solid component) that is made of a blend of dynamically vulcanized EPDM dispersed in a matrix of a thermoplastic polyolefin polymer. Either the first polymer structure or both the first and second polymer structures are blended with an effective amount of a semicrystalline random adhesive copolymer.
U.S. Pat. No. 7,326,471 B2 discloses an automotive sealant composite structure. The composite structure includes a first piece comprising a first elastomeric component that includes an at least partially crosslinked rubber, a first olefinic thermoplastic resin component, and a second olefinic thermoplastic resin component. The second olefinic thermoplastic resin component includes a propylene copolymer that has (i) 60 wt. % or more units derived from propylene, (ii) isotactically arranged propylene derived sequences, and (iii) a heat of fusion less than 45 J/g. The composite structure also includes a second piece at least partially adhered to the first piece. Preferably, the second piece includes one or more thermoset ethylene copolymer rubbers. Preferably, the first piece is a corner piece and the second piece is a straight piece at least partially adhered to the corner piece, together constituting a vehicular window seal structure.
Japanese Patent Publication No. 2005-088718 A provides a glass run channel for a vehicle capable of attaining effective weight reduction while maintaining sufficiently high mechanical strength. This glass run channel consists of a base portion and a lip portion. The base portion is a glass run channel for the vehicle formed out of foamed thermoplastic elastomer foamed at the time of extrusion molding with chemical foaming agent, gas, water or supercritical fluid, and has the following properties: apparent specific gravity of 0.5 to 0.8, torsional rigidity of 3.2 to 4.0 MPa, tensile strength of at least 4.5 PMa and elongation of at least 350%.
Japanese Patent No. 4660016 B provides a method for easily producing a lightweight molded item having a good external appearance. This method for producing a lightweight molded item comprises blending (A) a blowing agent masterbatch prepared by mixing 50-95 mass % thermoplastic rubber having a melt viscosity (at 190° C. and a shear rate of 100 s−1) of 101-105 Pa·s with 50-5 mass % blowing agent with (B) a thermoplastic resin having a melt viscosity lower than that of the thermoplastic rubber and heating the resultant blend to a temperature higher than the melting point of the thermoplastic resin to thereby foam and simultaneously mold the blend.
Thermoplastic vulcanizate is vulcanized thermoplastic elastomers where cross-linked rubber forms a dispersed, particulate, elastomeric phase within a thermoplastic phase of a stiff thermoplastic such that thermoplastic properties are achieved. Thermoplastic vulcanizates are conventionally produced by dynamic vulcanization. Dynamic vulcanization is a process whereby a rubber component is crosslinked, or vulcanized, under intensive shear and mixing conditions within a blend of at least one non-vulcanizing thermoplastic polymer component at or above the melting point of that thermoplastic. Typically, the rubber component forms cross-linked, elastomeric particles dispersed uniformly in the thermoplastic. See, for example, U.S. Pat. Nos. 4,130,535; 4,311,268; 4,594,390; and 6,147,160.
Thermoplastic vulcanizates can be used as a foaming material. Endothermic and exothermic chemical or physical foaming agents are blended to the thermoplastic base material. Many attempts have been made in the art to foam thermoplastic vulcanizates.
International Publication No. WO 2004/016679 A2 describes soft thermoplastic vulcanizate foams comprising a polyolefin thermoplastic resin, at least partially crosslinked olefinic elastomer, hydrogenated styrenic block copolymer, and optional additives. The soft foams are said to have smooth surfaces, low water absorption, improved compression set and compression load deflection.
International Publication No. WO 2007/0044123 A1 describes thermoplastic vulcanizates which can be foamed by employing supercritical foaming methods, including at least one cured rubber component, at least one conventional thermoplastic resin component, at least one random polypropylene copolymer, and at least one thermoplastic elastomer styrenic block copolymer.
U.S. Pat. No. 7,319,121 relates to foamed thermoplastic elastomer profiles comprising a foamable thermoplastic elastomer composition having a) a cross-linkable hydrocarbon rubber and b) a thermoplastic polyolefin resin having a Tm greater than 120° C. The composition further comprises: a) 25 to 30 wt. % of a partially or fully vulcanized reaction product of said cross-linkable hydrocarbon rubber with a cross-linking agent, said reaction product being present as a dispersed phase; b) 7 to 12 wt. % of said thermoplastic resin as a continuous phase; c) 8-22 wt. % of an elastomeric thermoplastic modifier; and, optionally, d) 3-12 wt. % solid filler; and/or e) 35-45 wt. % of non-aromatic hydrocarbon oil; where the composition has been prepared by dynamically vulcanizing said composition.
International Publication No. WO 2013/062685 A2 discloses a composition comprising a) a thermoplastic vulcanizate and b) a thermo-expandable microsphere comprising a polymer shell and a propellant encapsulated in said polymer shell based on the total weight of the composition. The composition is suitable for making foam with balanced load deflection and elasticity, including soft touch, reduced to low deflection, improved relaxation performance and low water absorption, replacing either soft paint or assembled constructions with foam sheets and meeting requirements in soft touch applications.
Other disclosure of thermoplastic vulcanizates or thermoplastic vulcanizate compositions can be found in U.S. Pat. Nos. 7,294,675 B2; 7,964,672 B2; 7,829,623 B2; 6,288,171 B2; 6,268,438 B1; and 6,399,710 B1.
However, while achieving the weight reduction of a foamed thermoplastic vulcanizate material, certain mechanical properties, such as tensile strength and tension set, of the foamed material tend to drop. These properties impact the sealing performance and service life of the automotive seal parts made therefrom. The surface of the foamed material and processing properties deteriorate, compared with non-foamed thermoplastic vulcanizate material, because some of the cells may come to the surface of the foam causing the surface to become rough. Also during foaming of the thermoplastic vulcanizate, cells may not be distributed evenly, which also results in poor proccessability.
There remains a need for compositions for foamed materials with improved tensile strength and tension set and while maintaining the weight reduction and certain properties including surface performance. Such compositions may provide desirable sealing performance of automotive seal parts made therefrom with reduced weight. Applicants have found that the above objectives can be achieved by combining a propylene-based elastomer with thermoplastic vulcanizate to prepare a foamed material, which can be used for manufacturing automotive seal parts. Applicants have also believed that the addition of the propylene-based elastomer can reduce the use amount of the foaming agent without compromising the foaming effects, thus, further lowering the cost for automotive seal parts.